1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and, more particularly, to a driving circuit-integrated LCD device with a large-scale panel and a fabrication method capable of fabricating a large-scale panel by implementing a low-resistance wiring.
2. Discussion of the Related Art
In today's information society the importance display of devices to present visual information is increasing, and in order to be successful in the marketplace, the display device must have low power consumption, thin profile, low weight, and high picture quality characteristics. A liquid crystal display (LCD), an important type of a flat panel display (FPD), can satisfy these conditions as well as being suitable for mass production, so various types of brand-new products have been introduced taking advantage of LCDs. Also LCDs are replacing cathode ray tubes (CRTs) in many applications.
In general, LCD devices display a desired image by controlling the light transmittance of liquid crystal cells by separately supplying a data signal carrying image information to the liquid crystal cells arranged in a matrix form.
Active matrix (AM) LCDs have liquid crystal in pixel areas that are driven using an amorphous silicon thin film transistor (a-Si TFT) as a switching device.
The concept of the amorphous silicon TFT technique was established by LeComber et al. of England in 1979 and commercialized as a 3-inch liquid crystal mobile TV. Recently, 50-inch or wider large-scale TFT LCD devices have been developed. In particular, because the amorphous silicon TFT is available as a low temperature process and can use an inexpensive substrate, it is widely used.
However, the electrical mobility of the amorphous silicon TFT cannot support a peripheral circuit requiring a high switching speed of 1 MHz or higher. Thus, research to integrate both the pixel part and the driving circuit part on a glass substrate by using polycrystalline silicon that has greater field effect mobility than the amorphous silicon TFT is being actively pursued.
Polycrystalline silicon TFTs have been used in small modules such as in camcorders since the liquid crystal color television was developed in 1982, because with its low photosensitivity and high field effect mobility, a driving circuit can be directly fabricated on the substrate.
The increase in mobility can enhance the operation frequency of the driving circuit that determines the number of pixels, and thus the image resolution of the display device can be facilitated. In addition, because time for charging a signal voltage of the pixel part is reduced, distortion of a transmission signal is reduced and thus the picture quality can be improved.
Further, the polycrystailine silicon TFT can be driven at a voltage lower than 10V compared with the amorphous silicon TFT having a high driving voltage (˜25V). Power consumption may also be reduced.
The structure of the LCD device will now be described with reference to FIG. 1.
FIG. 1 is a schematic plan view showing the structure of a related art LCD device, specifically, a driving circuit-integrated LCD device in which a driving circuit is integrated on an array substrate.
As shown, the LCD device includes a color filer substrate 5, an array substrate 10 and a liquid crystal layer (not shown) formed between the color filter substrate 5 and the array substrate 10.
The array substrate 10 comprises a pixel area 35, an image display region in which pixels are arranged in a matrix form, and a driving circuit 30 including a data driving circuit 31 and a gate driving circuit 32 positioned at the periphery of the pixel area 35.
Though not shown, the pixel area 35 includes a plurality of gate lines and a plurality of data lines vertically and horizontally arranged to define a plurality of pixel regions on the substrate 10, a TFT, a switching device, formed at each crossing of the gate lines and the data lines, and a pixel electrode formed in the pixel region.
The TFT, a switching device for applying or cutting off a signal voltage to the pixel electrode, may be a field effect transistor (FET) controlling the flow of a current by a field effect.
The driving circuit 30 area of the array substrate 10 extends beyond the color substrate 5 and is positioned at an outer edge of the pixel area 35 of the array substrate 10. In this case, the data driving circuit 31 is positioned at the longer side of the extended array substrate 10 and the gate driving circuit 32 is positioned at the shorter side of the extended array substrate 10.
In order to suitably output an input signal, the data driving circuit 31 and the gate driving circuit 32 use a TFT with a CMOS (Complementary Metal Oxide Semiconductor) structure, namely, an inverter.
For reference, a CMOS TFT is an integrated circuit having a MOS structure used for the driving circuit TFT that requires high speed signal processing, needs an N channel TFT and a P channel TFT, and has speed and density characteristics in between an NMOS and a PMOS.
The gate driving circuit 32 and the data driving circuit 31 supply a scan signal and a data signal to the pixel electrode through the gate lines and the data lines. Connected with an external signal input terminal (not shown), the gate driving circuit 32 and the data driving circuit 31 control an external signal input through the external signal input terminal and output it to the pixel electrode.
A color filter (not shown) that implements color and a common electrode (not shown) that is opposite the pixel electrode formed on the array substrate 10, are formed in the pixel area 35 of the color filter substrate 5.
A cell gap is prepared between the color filter substrate 5 and the array substrate 10, allowing the substrates to be uniformly separated by spacers (not shown), and the two substrates are attached by a seal pattern (not shown) formed at an outer edge of the pixel area 35 to thereby form a liquid crystal display panel. At this time, the two substrates 5 and 10 are attached to one another using an attachment key formed on the color filter substrate 5 or the array substrate 10.
Because the constructed driving circuit integrated LCD device uses the polycrystalline silicon TFT, it has excellent device characteristics including excellent image quality and fineness, and it consumes less power.
However, the driving circuit-integrated LCD device has disadvantages in that because the N type TFT and the P type TFT are formed together on the same substrate, its fabrication process is quite complicated compared with the amorphous silicon TFT LCD device in which only a single type channel is formed.
Meanwhile, the gate wiring and the data wiring are means for transferring a scan signal and a data signal, respectively, and in this case, a signal delay and disconnection need to be avoided.
Thus, a material used for the wirings must have a specific resistance below a certain level, resist oxidation, and prevent disconnects during the fabrication process.
However, the related art LCD has a problem in implementing a large-scale liquid crystal display panel that requires a low-resistance wiring.